A conceptual model of the effects of rainfall variability on groundwater recharge was developed and applied to a small forested catchment in semi-arid Tanzania. The model simulated dual-domain recharge through the soil matrix and macropores, and was based on daily values of rainfall and potential evapotranspiration. Three different land-cover conditions (forested-nondegraded, deforested-nondegraded, and deforested-degraded) were included in the study in order to simulate the large-scale deforestation and land degradation process now occurring in Tanzania. In addition, the alternative land covers were also considered in combination with three different rainfall regimes.

The results indicate the importance of macropore flow, particularly during dry years. The lack of macropores under deforested-degraded conditions reduces the simulated groundwater recharge to such an extent that it is less than under forested conditions. Simulating a climate change scenario shows that a small change in rainfall (-15%) can cause a large change in recharge (-45%).

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